Theory of Lone Pair-Sigma Bond Geminal Interactions

Theory of Lone Pair-Sigma Bond Geminal Interactions 

We shall first illustrate how the OEMO approach can be used to elucidate the effect of geminal interactions on the stability and shape of molecules. We shall utilize the molecule H2O as the model system and compare the relative stabilization of the linear and bent geometries. The analysis involves the construction of the sigma MO s of HjO from the AO s of O and the group orbitals spannh the two hydrogens. 

The interaction diagrams of Fig. 40 show the various orbital interactions which obtain in the two geometries. However, before we make a one-to-one comparison of these interactions, a few remarks regarding the effect of bending upon the hydrogen group orbitals is necessary. 

We shall now compare the various MO interactions in the two geometries. The following trends become immediately apparent  

Actually, the 2px a interaction changes significantly and, consequently, AH2 molecules with four valence electrons ate linear. 

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